Fuels cells produce electricity by converting reactants (e.g., fuel and an oxidizing agent) through electrochemical reactions. In recent times, fuel cells have grown in popularity as an attractive alternative to the internal combustion engine because they generate little or no pollutants. One type of fuel cell is a proton exchange membrane (PEM) fuel cell. PEM fuel cells have an ion exchange membrane, partially comprised of a solid electrolyte, disposed between an anode and a cathode. To produce electricity through an electrochemical reaction, hydrogen is supplied to the anode and air is supplied to the cathode. An electrochemical reaction between the hydrogen and the oxygen in the air produces an electrical current.
When a fuel cell system is shutdown, generation of electrical current by the fuel cell is no longer required. The electrical circuit is opened, thereby relieving the cell of an electrical load. However, upon and during shut-down of the cell, the presence of air on the cathode along with hydrogen fuel remaining on the anode can cause unacceptable anode and cathode potentials, resulting in corrosion in the catalyst and the catalyst assembly support and consequent degradation of the fuel cell and its performance.
Moreover, even after the fuel cell system is shutdown, there are still opportunities for air to enter the cathode of the fuel cell, thereby subjecting the fuel cell to harm. As an example, air flow into the fuel cell system can be induced by the wind. Wind can push air into the system inlet and through the deactivated compressor. Ultimately, such air can travel through the system to the cathode, thereby exposing the cathode to an oxidizing agent.
Another way in which air can flow into the fuel cell system after shutdown is buoyancy-driven air flow. Cathode exhaust gas (mainly composed of nitrogen (N2) and little or no oxygen (O2)) remaining in the fuel cell system at shutdown is warmer and lighter than ambient air. Thus, there is a general tendency for the cathode exhaust gas to rise, which, in a typical fuel cell configuration, results in the cathode exhaust gas travelling backward (i.e., upward) through the system toward the highest point of the system (i.e., the air inlet). Consequently, ambient air can be drawn in through the outlet of the system (e.g., an exhaust pipe in a vehicle application) by a stack effect. Such ambient air can also travel backward through the system to the fuel cell, exposing the cathode to air.
Thus, there is a need for systems and methods that can minimize such concerns.